I. Field of the Invention
The present invention relates generally to fluid control valves, and, more particularly, to a bidirectional control valve for controlling fluid pressure to and from a fluid powered device.
II. Description of the Prior Art
Fluid powered devices, such as fluid powered lifts and jacks, are widely employed in industry. Such devices are typically pneumatically or hydraulically powered and include an expansible chamber or fluid powered motor for converting pressurized fluid flow to mechanical movement. Thus, by connecting the device to a source of fluid pressure, the fluid device produces mechanical movement in one direction while, conversely, exhaustion of the fluid pressure from the fluid powered device produces mechanical movement in the opposite direction.
In order to pressurize the fluid power device at the desired level, a bidirectional control valve is usually connected between a source of fluid pressure and the fluid powered device. These control valves are selectively operable to connect the fluid powered device with the source of fluid pressure or, alternatively, to exhaust pressurized fluid from the fluid powered device. Such previously known values are conventionally actuated by solenoids, hand levers, push buttons, foot pedals and the like.
These previously known bidirectional control valves, however, have not proven entirely satisfactory in use. One disadvantage of the previously known bidirectional control valves is that the value member must be manually moved to its neutral or closed position following actuation. Failure to do so, however, requires the reverse operation of bidirectional control valve in order to return the fluid device to the desired position.
A still further disadvantage of many of the previously known bidirectional control valves, and particularly solenoid actuated valves, is that while the direction of fluid flow through the valve is controllable the flow rate is not. Consequently, with these types of previously known control valves, accurate positioning of the fluid powered device is difficult, if not altogether impossible. Moreover, when accurate position of the fluid powered device is required, the control valve must be actuated in a reiterative fashion until the desired position of the fluid device is obtained. Such a reiterative process is time-consuming in practice and, therefore, costly.
A still further disavantage of many of the previously known manually operated bidirectional control valves is that the control valve itself must be manually unseated against the force of the fluid pressure. Consequently, when the valve is used to control high pressure fluid sources, it is difficult for the operator to manually unseat the valve against the force of this fluid pressure. Furthermore, when the degree of actuation of the control valve is used to control the flow rate through the control valve, accurate actuation of the control valve, and thus accurate positioning of the fluid powdered device, is difficult to achieve.